COIL COATING PROCESS

Abstract: A process for surface coating of plane surfaces in which on the material with plane surface chlorine-free paint- and lacquer materials is applied as wet paint in two layers, each layer being dried separately before the application of the next layer and where the total plane layer thickness is 40-300 microns, and then a plastic sheet is applied by lamination directly on top of the hot paint surface.

Description: COIL COftTING PROCESS The invention relates to a continuous process for surface coating a of metal substrates having a generally planar surface, on a coil-coating line for providing a durable and corrosion protecting coating on the metal surface. In the process paint- and lacquer materials are applied in two layers on the metal substrate with generally planar surface. These layers are applied as wet paint layers, which in dried state will have a certain degree of thermoplasticity. The first layer is a chlorine-free primer coat, such as e.g. an acrylic, epoxy or polyester coat. As the second layer on the primer coat, a chlorine-free, plastisol of an acrylic resin or of a polyester is applied as a paint layer. Said such wet paint layer is dried after application and has in the dried condition a certain degree of thermoplasticity. The paints are applied according to conventional techniques, such as roller coating, spray coating, curtain coating, etc. The drying is also performed by conventional methods, such as IR-tubes induction or convection heating. After the paint layers have been dried to a state of a certain degree of thermoplasticity, a chlorine-free plastic sheet or foil is applied directly upon the hot paint surface. The plastic sheets applied directly upon the hot paint surface by lamination, e.g. using a pressure roller, are made of various suitable pore-free, and chlorine-free foil materials, such as sheets of fluorocarbon polymers, e.g. PVF, PVF 2 , of acrylic resins, of polyesters or of polyurethanes. The plastic sheet and the second coat material together with the primer coat, build up a barrier which provides a very good corrosion protection to the metal substrate and the total thickness of the primer and the second coat should be from ' 40 to 300 microns. Thus, by the surface coating process according to the invention, a surface coating with extraordinary hardness and wear resistance is obtained which provides an extraordinary corrosion protection to the underlying substrate material. It is previously known to treat metal sheeting, e.g. coming from a coil, by painting with a primer layer and by applying a topcoat on top of the primer layer. However, only a limited degree of corrosion resistance of the so-coated metal sheet is thereby obtained, due to a certain porosity in the coating layer materials. It is also previously known to treat the surface of e.g. metal sheet by first applying an adhesive layer of 5-10 microns -and then applying a plastic sheet. Even in this case, a limited corrosion resistance is obtained owing to the fact that adhesive layer is so thin. Furthermore, it is previously " known from EP 0.233.-179 to use PVC-plastisols as layers on metal sheets and also PVC-foils as the uppermost layer. However, this gives rise to pollution problems when chlorinated materials are broken down either in service or when recycled and also gives rise to an impaired bonding of the total coating to the underlying metal substrate over time owing to migration of plasticizers such as phthalates to the interface between the metal substrate and the coating. As metal materials with generally planar surfaces which can be treated with the surface coating process according to the present invention, such materials as cold rolled steel, metallized steel, stainless steel, galvanized steel, aluminium, etc. are suitable. In the coating of sheet metal materials, the sheet metal is preferably pretreated chemically by usual methods such as pickling, phosphatizing, chromating etc. The layers of paint- and lacquer material consist of one primer layer and a second paint layer which can be pigmented or unpigmented. In said lamination the temperature of the metal sheet is from 150 up to 300 β C. In the process according to the invention a lamination without the use of any special adhesive is attained in one and the same process which gives a wear and corrosion resistant coating firmly bonded to the metal substrate by means of the second paint layer and first primer layer. The invention is more closely illustrated in the following examples: Example 1 In a conventional co ' il coating line the following is applied on 0.8 mm hot galvanized steel, chemically pretreated with "Bonder 1303" (a phosphatising agent from Metallgesellschaft GmbH, Germany); First layer: An epoxy primer ("KE 215-1003 Coilon primer" from Becker Industrifarg AB, Marsta, Sweden) is applied by reverse roller coat to a thickness of 6-8 microns dry film, drying/curing at 225°C PMT (peak metal temperature) and cooled. Second layer: On the previous layer an acrylic plastisol (68815-12 Coilon Plastisol from Becker Industrifarg AB, Marsta, Sweden) is applied to a thickness of 80 microns dry film. By reverse roller coat, drying/curing at 240°C PMT. Third layer: Directly upon the previous hot layer, a plastic sheet of acrylic resin (Korad 73002 from Polymer Extruded Products" Inc. newark N.J. USA) and a thickness of 50 microns is applied. A coating is obtained which provides excellent corrosion protection, high hardness and excellent wear resistance. Example 2 The same as Example 1 with following exceptions: Instead of hot galvanized steel, pretreated with "Bonder 1303", Alu-zink coated steel is used. As first layer is used an epoxy primer (KE216-1003 from Becker Industrifarg AB, Marsta, Sweden), instead of KE215-1003. A coating is obtained which provides excellent corrosion protection, high hardness and excellent wear resistance. Example 3 The same as Example 1 with the following exception: As third Tayer is used a plastic sheet of polyester resin (Hostaphan RNH 50 from Hoechst Aktiengesellschaft Germany) instead of Korad. A coating is obtained which provides excellent corrosion protection, high hardness and excellent wear resistance.

Claims: CLAIMS 1. A continuous process for surface coating a generally planar metal surface of a sheet or coil in a coil coating line, comprising the steps of: applying a chlorine-free primer first coat onto a generally planar metal surface of a sheet and drying said primer coat; applying a layer of polymer-containing wet paint as a second coat; drying said wet paint second coat by application of heat to a state of a certain degree of thermoplasticity to provide a barrier coating above said metal surface of thickness from 40 to 300 microns; applying a pore-free plastic sheet directly on top of said still hot paint coating and laminating, thereby forming a wear resistant and corrosion resistant coating, characterized in that as the second layer a chlorine-free plastisol of an acrylic resin or of a polyester is applied and as the pore-free plastic sheet a chlorine-free plastic sheet or foil of an acrylic resin, a fluoropolymer, a polyester or a polyurethane is applied. 2. A process according to claim 1, characterized in that the polymer resin in the second layer is an acrylate resin. 3. A process according to claim 1 or 2, characterized in that the plastic sheet or- foil is a sheet or foil of an acrylate resin. 4. A process according to any of claims 1-3, characterized in that the plastisol applied as the second layer contains a pigment and the plastic sheet is a clear plastic sheet. 5. A process according to any of claims 1-3, characterized in that the plastic sheet is pigmented.

Inventors: NAGLITSCH GERULF, NAGLITSCH, GERULF
Applicants: BECKER IND AB, NAGLITSCH GERULF, BECKER INDUSTRIFAERG AB, NAGLITSCH, GERULF
Application year: 1994
Main classification: B05D7
IPC codes: B05D7, B32B15